Generally, ultrasound transducers are used in ultrasound imaging devices for imaging in a wide variety of applications, especially medical diagnosis and treatment. Ultrasound imaging devices typically employ mechanisms to transmit scanning beams of ultrasound energy and to receive the reflected echoes from each scan. The detected echoes are used to generate an image which can be displayed, for example, on a monitor.
A typical ultrasound transducer comprises an acoustic element which transmits and receives ultrasound waves. The acoustic element may be made of a piezoelectric or piezostrictive material, for example. The acoustic element has a front side from which ultrasonic waves are transmitted and received, and a back side which may be bonded to an acoustic backing layer. An acoustic backing layer dampens the acoustic element to shorten the pulse length, or ringdown as it is often termed and to allow the transmission and reception in one direction. To produce this effect, the acoustic backing layer is typically made of a material having an attenuative nature. Hence, conventional materials used as a backing layer have been dense materials such as tungsten and epoxy.
A significant drawback to using a dense backing layer material is that a large amount of power consumed by the acoustic element is lost in the backing layer rather than being used to transmit ultrasound waves. If 3 dB of the transducer signal is attenuated on the backing material, the equivalent of half the power drawn by the acoustic element is lost. In other words, if the transmission efficiency of the ultrasound transducer is increased by 3 dB, the power needed to drive the transducer can be cut in half for the same signal output.
In order to reduce the amount of power lost in the backing layer, transducers having air backing layers have been used. An air backing layer reflects all the power directed out of the back side of the acoustic element toward the front side of the acoustic element. This occurs because of the impedance mismatch between the air and the acoustic element. The acoustic element may be cut to the right thickness so that the reflected ultrasound wave is in phase with an ultrasound wave originally directed to the front side of the transducer.
There are several significant disadvantages associated with an air back transducer. One is that an air back transducer has a longer ringdown time than a transducer having a dense backing layer. It is also very difficult to support an acoustic element in air.
Therefore, there is a need for an improved ultrasound transducer which provides effective damping of the acoustic element to reduce ringdown, electrically insulates the ultrasound transducer, and reduces the amount of power lost in the backing layer.